This invention relates generally to an apparatus and method for monitoring waveforms, and more particularly, to an apparatus and method for noninvasively monitoring the blood pressure waveform in a blood vessel by detection of the deformation of a diaphragm placed over tissue covering the blood vessel.
Methods for accurately monitoring the blood pressure waveform have been under investigation for some time. While invasive methods can provide accurate waveforms, the trauma caused the patient makes the technique undesirable in many cases. One such method involves the use of a fluid filled catheter inserted into the patient's artery. While accurate blood pressure measurements can be obtained by use of this method, the negative effects on the patient may, in many cases, outweigh the accuracy in results to be obtained by use of the method.
Another method to monitor a patient's blood pressure waveform is the widely used auscultatory method of Korotkoff. This method is noninvasive; however, it only provides a measurement of systolic and diastolic pressure on an intermittent basis; it does not provide the entire waveform on a continuous basis. Furthermore, use of this method often yields inaccurate results.
The tonometric method of measuring blood pressure is noninvasive and thus is an improvement over invasive techniques and in addition, it is also more accurate than the auscultatory method discussed above. Furthermore, it has the capability of providing the entire blood pressure waveform, as opposed to only the systolic and diastolic pressures provided by the auscultatory method discussed above.
In a prior type of arterial tonometer, an array of individual transducer elements is placed directly on the tissue overlying an artery or blood vessel from which blood pressure is to be determined. The elements directly sense the mechanical forces in the tissue with which each of them is in contact. The elements of the array are dimensioned and spaced apart from each other such that a plurality of these elements is required to cover the entire diameter or width of the underlying blood vessel; i.e., the size of each element is designed to cover only a small fraction of the diameter of the underlying blood vessel. The pressure of the array against the tissue is increased to properly applanate the underlying vessel but without causing occlusion. The fluid pressure within the artery is then conducted through the vessel wall and the overlying tissue to the transducers.
It has been found that with the conventional tonometer, a continuous contour of the tissue stresses under the array is not obtained due to the use of discrete elements. Additionally, it is believed that in prior methods, no compensation means is provided for motion artifacts which may affect the forces translated to the sensors from the artery.
Thus, it would be desirable to provide a tonometer system and method for monitoring the pressure in a vessel, such as an artery, which is noninvasive and is capable of faithfully transducing the vessel pressure waveform.
It would also be desirable to provide a tonometer system and method which can compensate for artifacts which may tend to decrease the accuracy of the tonometer in monitoring the waveform.
It would also be desirable to provide a tonometer system and method which has improved reliability and repeatability of pressure waveform measurements.
The present invention addresses these needs.